1. Field of the Invention
The present invention relates to a rolling bearing and particularly to a rolling bearing consisting of carburized steel.
2. Description of the Background Art
Carburized steel commonly used as a bearing material has a longer rolling contact fatigue life than bearing steel. Thus a rolling bearing made of carburized steel is generally used as a long life bearing.
A long life of a carburized steel bearing is assumed to be attributable to a large amount of retained austenite produced by carbulizing and the presence of compressive residual stress in its surface layer. It is assumed that a conventional steel product has a large amount of non-metallic inclusion, which acts as a source of stress concentration, whereas in the carburized steel rolling bearing, compressive residual stress and retained austenite produced by carburizing of the surface layer serve to relax the stress concentration.
Recent development in steelmaking technique, however, has resulted in the improvement in steel quality and has enhanced the life of bearing steel. Thus the advantage of carburized steel over bearing steel in terms of service life has almost eliminated.
Although it has been known that carburized steel(e.g. M50NiL steel) containing a large amount of Cr(chromium), Mo(molybdenum) and/or V(vanadium), exhibits a life even longer, the use of these expensive chemical components, such as Cr, Mo, and V is not practical.